From the viewpoint that a fluororesin powder such as polytetrafluoroethylene (PTFE) has low surface energy of a fluororesin and is water repellent and oil repellent, and has a large specific gravity, it is very difficult to disperse the fluorine resin powder in a nonaqueous liquid medium such as an organic solvent. In this regards, in the related art, a compound having a long chain perfluoroalkyl group having 8 or more carbon atoms has been used as a dispersant for fluororesin so as to enable dispersion in the aqueous liquid medium.
However, in recent years, a long chain perfluoroalkyl group having 8 or more carbon atoms has a concern with persistence to the environment, accumulation, and toxicity to the living body. As a dispersant which can be used instead of such a compound having a perfluoroalkyl group having 8 or more carbon atoms, for example, a dispersant for fluororesin having a specific structure disclosed in PTLs 1 to 3 has been used.
In a case of using such a dispersant, even with the dispersibility of the fluororesin, there were problems in that dispersion stability is insufficient, a compound having a structure such as amide or sulfonamide contained in the dispersant causes deterioration of electrical properties when being used for an electronic member, and it is not compatible with other binder resins when being used for a coating film, and thereby a smooth coating film cannot be obtained.
Meanwhile, the electrophotographic photoreceptor is repeatedly used in an electrophotographic process, that is, in cycles of charging, exposure, development, transfer, cleaning, static elimination and the like, and undergoes various stresses during that period. Examples such stresses include mechanical stress such as rubbing with a cleaning blade, magnetic brush or the like, abrasion on a surface of a photosensitive layer due to contact with a developer, paper or the like, scratches, and peeling of the film. The damage due to such mechanical stress tends to appear on an image and directly impairs image quality, which is a major factor limiting a life span of the photoreceptor.
Various studies have been made as means for the mechanical stress of the photoreceptor. For example, a protective layer is provided on an outermost surface layer of the photoreceptor, the mechanical strength of the binder resin is made enhanced in the outermost surface layer, and a filler is added to the outermost surface layer. Among them, study of using fluororesin particles as a filler has been made (for example, PTL 4). The fluororesin particles have high lubricity and have a role of improving the abrasion resistance of the photoreceptor by reducing a frictional force generated when the photoreceptor and a member are in contact with each other during the electrophotographic process.
Since there is a problem in that the dispersibility becomes poor even in a case where the fluororesin particles are used for the electrophotographic photoreceptor, a dispersant has been used (for example, Patent Literatures 5 and 6).